1. Field of Invention
This invention relates to a cap for plastic containers such as dairy and drink bottles and, in particular, to a snap-on cap which converts by the consumer to a twist on/off reclosure lid.
2. Brief Statement of the Prior Art
Caps for liquid containers are commonly molded of plastic and are of two basic types. One type is a twist-on, or screw, cap with a peripheral skirt having a helical thread which engages a threaded neck finish of the container and is applied by threading it onto the neck of the container. The other type is a snap-on cap which has a peripheral skirt which has one or more annular beads on its inside wall that snap into receiving grooves of the neck finish of the container when the cap is pressed onto the neck of the container. Both types of caps are rendered tamper-evident by the inclusion of a lowermost annular bead that seats into a groove of the container neck with score lines in the skirt to permit the consumer to sever the cap into a reclosure lid and a throw away tear band.
Unfortunately, there are disadvantages to each type of cap. While the snap-on cap offers the advantage of simple bottling and capping machinery, the reclosure lid which is formed when the tear band is removed by the consumer cannot be tightly sealed to the container neck. The twist-on cap forms a reclosure lid which can be twisted to compress the container neck tightly against a gasket in the lid by the consumer, however, complex capping machinery is required for the bottling operations as the containers or caps must be rotated during application of the caps.
The difficulties in sealing with snap-on caps is exacerbated by wear of the dies, shear steel and neck rings, used in blow molding of the plastic containers which result in imprecise dimensions of the critical dimensions of the neck finish.
Gaskets of various designs have also been used for the caps to improve their sealing to the containers. Foil discs have been ultrasonically and thermally bonded to bottle necks, however, their application increases manufacturing and bottling costs.
In my prior patent, U.S. Pat. No. 4,032,029, I disclosed a closure with an annular tear band and tab, and an annular lip. While this closure was a substantial improvement over the aforementioned closures, its manufacture require a split cavity mold, and it also utilized a less than ideal center corking skirt.
In my prior patents, U.S. Pat. Nos. 4,632,265 (Re. 33,764); 4,951,830; 5,207,340; and Des. 329,602 and 342,897, I disclosed press-on caps with an annular tear band and radially projecting tear tab which can be molded in a manufacturing mold having a single parting surface. In my prior patent, U.S. Pat. No. 4,819,906, I disclosed and claimed the mold useful to manufacture the caps.
All of these prior press-on caps formed a press-on reclosure lid when the consumer opened the bottle by pulling on the tear tab.